1. Field of the Invention
The present invention generally relates to a rotor for a rotating electric machine, such as alternating current (a.c.) generators and electric motors. More particularly, the present invention relates to rotary electric machines, which are adapted to hold permanent magnets with a resin-made magnet holding member, where the permanent magnets are disposed between circumferential side faces of two adjacent claw-like magnetic doles of Lundell-type pole cores, for instance.
2. Related Art
In a conventional rotor for an a.c. generator, for example, it is known that each permanent magnet in the generator is inserted between the circumferential side faces of two adjacent claw-like magnetic poles of Lundell-type pole cores to diminish the magnetic flux leakage between a plurality of claw-like magnetic poles. At the same time, the magnetic flux of the permanent magnets is directed towards the field coil (field winding) to improve the output efficiency, i.e., the electric power generating efficiency of the stator coil (armature winding) against the magnetomotive force of the field coil.
When Lundell-type pole cores rotate, strains are generated on the permanent magnets in the direction of the centrifugal force. Therefore, conventional devices require an arrangement where the permanent magnets do not protrude from the area between the circumferential side faces of two adjacent claw-like magnetic poles.
Such a technique is disclosed in, for example, Japanese Unexamined Patent Publication No. 4-165950. This document teaches that the outer face of a rotor, i.e., the outer peripheral face of a plurality of claw-like magnetic poles of Lundell-type pole cores, and the outer faces of permanent magnets, are covered with a non-magnetic holding member made of a metal such as aluminum. Furthermore, another technique is disclosed in Japanese Unexamined Patent Publication No. 3-265450. This document discloses that a metal or resin-made non-magnetic ring is disposed between claw-like magnetic poles of Lundell-type pole cores so that the permanent magnets are held by the non-magnetic ring.
According to the technique disclosed in Japanese Unexamined Patent Publication No. 4-165950, which employs a construction where the outer peripheral face of a rotor is covered with a non-magnetic holding member, a problem exists in that the air gap expands between the outer peripheral faces of the Lundell-type pole cores and the internal peripheral face of the stator core. Thus, the output efficiency, i.e., the electric power generating efficiency of the stator coil, is degraded by the expanding air gap between the outer peripheral faces of the Lundell-type pole cores and the internal peripheral face of the stator core.
Furthermore, the metal-made non-magnetic holding member and the permanent magnets are mounted on the Lundell-type pole cores, which are subjected to the magnetomotive force produced by the field coil. Accordingly, another problem exists, in that high-frequency impact magnetic noise caused by metallic collision noise is made between the claw-like magnetic poles and the non-magnetic holding member due to the vibration conveyed from the Lundell-type pole cores when the Lundell-type pole cores are rotated by rotation of the shaft.
Furthermore, in the technique disclosed in Japanese Unexamined Patent Publication 3-265450, as the non-magnetic ring is formed to have a circular shape with a constant width, strains are generated which deform the non-magnetic ring radially inwardly when a difference in thermal expansion exists between the non-magnetic ring and the claw-like magnetic poles. The non-magnetic ring is often deformed or broken.